Conventionally, automobiles for which quietness of engine behaviors is regarded as important, include engines in which explosion occurs at equal (regular) intervals. The engine in which explosion occurs at equal intervals commonly uses a method in which a physical amount (e.g., an angular acceleration rate, rotational speed) indicating a decrease amount of an engine speed due to occurrence of a misfire is measured at a next time point of the normal ignition of a misfire cylinder (at a time point immediately before the normal ignition), and it is determined whether or not the misfire has occurred in the cylinder at this time point (see e.g., Patent Literature 1 or the like). In the engine in which explosion occurs at equal intervals, the decrease amount of an instantaneous angular velocity of a crankshaft between a normal (non-misfire) state (a state in which no misfire has occurred) and a misfire state (a state in which the misfire has occurred) becomes greatest, at a time point immediately before the next timing of normal ignition. Therefore, it is determined whether or not the misfire has occurred in the cylinder based on the decrease amount of the instantaneous angular velocity of the crankshaft at a time point immediately before the ignition timing.